Conventional technology has been developed for recording information both in the land and in the groove to improve the track density of an optical disk as a recording medium. For example, Japanese Laid-Open Patent Application No. 5-314538/1993 (Tokukaihei 5-314538) discloses a method of forming a track for storing information both in the land and in the groove thereof.
Referring to FIG. 27, a magnified view of an optical disk, the following is an explanation about the method of forming a track disclosed in the above laid-open patent application. An optical disk 101 has a groove 102, 104, 106, etc. and a land 103, 105, etc. provided alternately to form respective information recording tracks. For example, a sidewall 108, one of the sidewalls of the groove 104, wobbles according to, for example, rotation synchronization information and address information. In other words, the sidewall 108 stores therein a wobble signal that is FM-modulated from the rotation synchronization information and/or address information.
The optical disk 101 is configured so that the distance between the adjacent wobbling sidewalls (e.g., the distance between the sidewall 108 and an adjacent wobbling sidewall 107 of the groove 102, or the distance between the sidewall 108 and another adjacent wobbling sidewall 109 of the groove 106) is longer than the diameter of a light beam 110. Therefore, the light beam 110 is prevented from reading out the wobble signal stored in the sidewall 107 and 109.
With the optical disk 101 configured as above, as the optical beam 110 tracks, for example, the groove 104, a wobble signal is reproduced from the sidewall 108 of the groove 104. Rotation synchronization information and address information are read out of the wobble signal to control rotation of the optical disk and reproduce address information. In this case, the distance between the wobbling sidewall 108 of the groove 104 and the wobbling sidewall 109 of the adjacent groove 106 is set to be longer than the diameter of the optical beam 110. Therefore, the periphery of the light beam 110 is configured not to reach the sidewall 109 when the groove 104 is tracked. Therefore, the wobble signal of the sidewall 108 of the groove 104 is not interfered by the wobble signal of the sidewall 109.
When the land 103 is tracked, a wobble signal is reproduced out of the sidewall 108 in the same manner as above. In this case, since only the sidewall 107 of the adjacent groove 102 wobbles and is located opposite from the land 103, the periphery of the light beam 110 does not reach the sidewall 107 when the land 103 is tracked. Therefore, the wobble signal of the sidewall 108 of the land 103 is not interfered by the wobble signal of the sidewall 107.
Consequently, if the optical disk 101 configured in the above manner is used, the cross-talk of the wobble signal is reduced, the rotation of the optical disk 101 is surely controlled, and the address information is precisely read out. Hereinafter, the track in which a wobble signal is stored only in one of the sidewalls of the land and of the groove will be referred to as a one-side wobbling track. Therefore, the groove 104 and the land 103 oppositely sandwiching the wobbling sidewall 108 have the same rotation synchronization information and address information.
A well-known method of improving the recording density of an optical disk is a constant liner velocity (CLV) method. Referring to FIG. 28, the following is an explanation about information recording/reproducing device that carries out the CLV recording with respect to an optical disk of a one-side wobbling track.
First, to record information with the CLV method, a wobble signal including rotation synchronization information is stored with the CLV method into one of the sides of the track of the optical disk 101 in advance. An optical pickup 111 radiates a light beam to the optical disk 101 provided with a wobbling track, and extracts a wobble signal aa out of a track error signal or a total signal that are reproduced from the reflected light. The wobble signal aa is inputted to an address information reproducing section 112 and to a CLV rotation control section 113. Then a clock cc of a constant frequency is inputted from a crystal oscillator 114 to the address information reproducing section 112 and to the CLV rotation control section 113.
Next, in the address information reproducing section 112, address information is FM-modulated from the wobble signal aa according to the clock cc. The CLV control section 113 compares the phase of the rotation synchronization signal included in the wobble signal aa and the phase of the clock cc, and outputs a drive signal bb to a spindle motor 115 so that the phases synchronize. The rotation of the optical disk 101 is controlled in this manner. Since the wobble signal aa is stored with the CLV method, the rotation of the optical disk 101 can be controlled with the CLV method.
Incidentally, in order to access recording information at high speeds, the position where the recording of the information starts needs to synchronize with the rotation of the disk and thus always the same. In this manner, the address in search can be found by predicting the rotation of the disk during the search for information, thereby enabling high speed search. Japanese Laid-Open Patent Application No. 4-184718/1992 (Tokukaihei 4-184718), "OPTICAL DISK AND OPTICAL DISK DEVICE", discloses a method of storing a reference position in the optical disk in advance in the above manner, and determining the position where the recording of the information starts according to that reference position. Referring to FIGS. 29 and 30, the following explains the above method.
In the optical disk 120, the groove 121 sandwiched between the land 123 and 124 functions as a track for recording/reproducing the information. The track 121 has an index mark 122, a wobbling once for every round, that is stored when the track 121 is formed in the optical disk 120.
A comparator in a device (not shown) for reproducing the optical disk 120 compares a track error signal dd read out of the index mark 122 and a slice level ee to obtain an index mark detection signal ff (reference signal). The index mark detection signal ff functions as a reference for the absolute position once for a round of the optical disk 120. The index mark detection signal ff can format the address information in synchronization with the rotation of the optical disk 120.
The length of the index mark 122 is set to be approximately equal to an information recording bit, and has a position detection precision of less than the length of the information bit (not more than 1 micron). In other words, the position where the recording of the information starts is lined up once for every round highly precisely by storing the index mark 122 in advance.
However, even if the position where the recording of the information starts is determined, the positions of the recording bits thereafter vary depending on a variation of the rotation of the optical disk. When the recording is completed, the variation have been accumulated and greatly changes the position where the recording ends. Therefore, the position where the recording ends and a position where the next recording starts may overlap.
Therefore, a conventionally typical method of avoiding the overlapping with the position where the next recording starts is to shift forward in advance the position where the recording ends, and to thus provide a so-called gap area (or sometimes referred to as a buffer area) before the position where the next recording starts so as to compensate for the variation.
As the position where the recording ends varies, a position of the reproducing clock for reproducing the recording data shifts every time at the position where the next recording starts. Therefore, it is necessary to lead in a phase locked loop (PLL) every time the reproducing clock position shifts. Therefore, an area to which the PLL is led in is provided at the beginning of the recording data area of the optical disk 120.
Since the above-mentioned gap area and lead-in area for the PLL reduces the utilization factor of the recording area, there occurs a problem that the recording capacity of the optical disk is reduced. The ratio of the reduction to the total capacity is about 9%, according to Japanese Industrial Standards for present rewritable optical disks.
Moreover, when a target address is searched for, optical disks having the above one-side wobbling track have a problem that the land and the groove oppositely sandwiching the wobbling sidewall carry the same address information and cannot be distinguished from each other. In other words, if an address is designated when information is recorded or reproduced, there exist two identical addresses, thus causing inconvenience in address management.